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Citation
Tags
HERO ID
2003205
Reference Type
Journal Article
Title
Increases in corticospinal responsiveness during a sustained submaximal plantar flexion
Author(s)
Hoffman, BW; Oya, T; Carroll, TJ; Cresswell, AG
Year
2009
Is Peer Reviewed?
Yes
Journal
Journal of Applied Physiology (1985)
ISSN:
8750-7587
EISSN:
1522-1601
Volume
107
Issue
1
Page Numbers
112-120
Language
English
PMID
19443741
DOI
10.1152/japplphysiol.91541.2008
Abstract
Studying the responsiveness of specific central nervous system pathways to electrical or magnetic stimulation can provide important information regarding fatigue processes in the central nervous system. We investigated the changes in corticospinal responsiveness during a sustained submaximal contraction of the triceps surae. Comparisons were made between the size of motor-evoked potentials (MEPs) elicited by motor cortical stimulation and cervicomedullary motor-evoked potentials (CMEPs) elicited by magnetic stimulation of the descending tracts to determine the site of any change in corticospinal responsiveness. Participants maintained an isometric contraction of triceps surae at 30% of maximal voluntary contraction (MVC) for as long as possible on two occasions. Stimulation was applied to the motor cortex or the cervicomedullary junction at 1-min intervals during contraction until task failure. Peripheral nerve stimulation was also applied to evoke maximal M waves (M(max)) and a superimposed twitch. Additionally, MEPs and CMEPs were evoked during brief contractions at 80%, 90%, and 100% of MVC as a nonfatigue control. During the sustained contractions, MEP amplitude increased significantly in soleus (113%) and medial gastrocnemius (108%) muscles and, at task failure, matched MEP amplitude in the prefatigue MVC ( approximately 20-25% M(max)). In contrast, CMEP amplitude increased significantly in medial gastrocnemius (51%), but not in soleus (63%) muscle and, at task failure, was significantly smaller than during prefatigue MVC (5-6% M(max) vs. 11-13% M(max)). The data indicate that cortical processes contribute substantially to the increase in corticospinal responsiveness during sustained submaximal contraction of triceps surae.
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